Various prior art techniques have been developed to attempt to produce a uniform or other desired illumination pattern on an illuminated surface. For example, reflective sheet metal then bent to a desired shape have been designed to be incorporated into an optic using one or more LED's. The term optic is intended to include conventional reflectors and refractive optical elements as well as focusing/defocusing lenses. These optics are typically relatively thin (e.g. 1/32 inch or less) so that it is easily bent to the final form. Acrylic plastic (formed and molded) has also been used. However these optics at present cannot be formed with adequate optical precision to reflect or direct light accurately to a selected location on a surface. These optics can therefore have efficiencies of less than 50%. Part of the problem with prior art designs when applied to a LED emitter are that they do not account for the characteristics of LED's which are virtually a point source of light and therefore magnify the effect of low precision optics.
Prior art optics have not provided direct conduction of heat form the LED through the optic. The LED is positioned on a circuit board and therefore heats the circuit board that drives the LED and can cause early failure from overheated components or require an over sized heat sink on the rear of the circuit board for heat dissipation.
The use of LED's for illumination (as opposed to the display of a condition) has rapidly evolved, however there has not been a solution to the problem of using LED's to achieve uniform illumination over a specified area.
All LED's use a relatively small amount of power and generate a relatively small amount of heat. A single LED is nearly a point source of light and can be installed in a fixture using a conventional parabolic reflector (as in a flashlight) to produce a highly focused beam. LED's have also been utilized for room accent lighting, such as recessed can lights or track lights. This use of LED's in those applications has been limited to circumstances where an even distribution of light is not essential. Multiple LED's have been utilized in the same fixture, using the same reflector to “aim” the LED light into spot beams in such a way as to create a wider illuminated area, however the areas between spot beams are not uniformly illuminated so that LED's have been limited to those applications where uniformity of illumination is not an issue.
A common lighting requirement is in display cases and art illumination. These two applications are often referred to as display lighting. Presently display lighting applications are met by fluorescent tubes and elongated incandescent bulbs using a single filament and mounted in a fixture with an elongated reflector. Because the illumination emanates from an elongated source and assuming an illumination area that has a length no greater than the length of the bulb or tube, the illumination from these fixtures is the best that can be achieved with current technology. In these applications a cylindrical reflector produces poor illumination uniformity over a fairly narrow angular range and highly inefficient light flux and uses lighting technology that generates substantial heat.
The problems of the inefficiency of incandescent lighting and the somewhat better efficiency but lower quality of light (narrow spectrum and glare) from fluorescent lights are well known but no one has devised a way to satisfy the requirements of display lighting with any known technology. LED lights are efficient in generating light (good lumens) and produce relatively little heat but because they are a near point light source they have been thought to be impractical for display lighting and other applications were wide dispersion of light is required. As used herein “near point source” should be taken to mean a source of light that emanates from an source of illumination that is very small as compared to the dimension of the fixture that directs the light.